How political ads can elect a president

[Commentary] Television spots are the medium through which the modern campaign is fought. The success or failure of the candidates at producing effective advertisements could have a huge influence on the outcome in November. Each side of the campaign will spend inordinate amounts of money to pay for 30-second advertisements -- which will also be spread through the Internet -- that seek to define the message of the campaign of 2012 and the terms of the fight.

[Zelizer is a professor of history and public affairs at Princeton University]